The high profile death of actress Natasha Richardson - Liam Neeson's wife - following a skiing accident in Canada in March 2009 highlights how dangerous head injuries can be.

Unlike Michael Schumacher, she was not wearing a helmet. A helmet helps protect the skull, but injury is still possible.Skiers who collide at speed with other people or hard objects, such as trees or rocks, can sustain serious damage.

Such injuries may include skull fractures and bleeding and swelling in and around the brain.The build-up of pressure on the brain can cause serious complications needing urgent treatment.

Primary concerns include insuring a good oxygen and blood flow to the brain and the rest of the body, while controlling the pressure.